1. Technical Field
This invention relates to augmented gas turbine engines in general, and more specifically to apparatus for distributing fuel within an augmented gas turbine engine.
2. Background Information
Augmentors, or "afterburners", are a known means for increasing the thrust of a gas turbine engine. Thrust is produced within a gas turbine engine by compressing air with a fan and a compressor, adding fuel to the air within a combustor, igniting the mixture, and finally passing the combustion products (referred to as core gas) through a nozzle. A turbine positioned between the combustor and the nozzle extracts some of the energy added to the air to power the fan and compressor stages. In an augmented gas turbine engine, additional thrust is produced by adding fuel to the core gas exiting the turbine and igniting the mixture. An augmentor fuel pump supplies pressurized fuel to an augmentor fuel control which, in turn, distributes the fuel to a plurality of spray manifolds (or spray bars, nozzles, or the like) positioned within the core gas flow path aft of the turbine. The position of the spray manifolds within the core gas flow path promotes uniformity in the distribution of fuel. Mechanical flame holders are positioned downstream of the spray manifolds to create low velocity wakes where flame can be initiated and maintained.
The high temperature core gas exiting the turbine provides a severe thermal environment for the spray manifolds. Fuel left in the spray manifolds after augmentor demand has been canceled will thermally degrade and leave an undesirable residue, typically in the forms of solids, varnish, and gum-like materials. The solid residue is often referred to as "coke". The residue deposits can foul fuel injection sites within a spray manifold and/or clog the lines connecting spray manifolds to the fuel control. To minimize residue deposits, spray manifolds are typically provided with drains for dumping any fuel that remains in the spray manifolds and/or lines connecting the spray manifolds to the fuel control after augmentation. The dumped fuel atomizes within the core gas flow and exits the engine unburned with the exhaust. In some instances, however, fuel remains in the spray rings even after dumping is complete. The stationary residual fuel is particularly susceptible to the formation of residue.
What is needed, therefore, is an apparatus for distributing fuel in an augmentor that minimizes residue deposits within the fuel spray manifolds, and one that cleans any residue deposits that do form.